Java error whenever attacking mobs

[Zyroh]

Each time anyone attacks a mob this error pops up in the client as well as in the error log for the server.  not sure what the source of it is, please help.

Jun 13, 2009 2:53:59 PM net.sf.l2j.gameserver.model.quest.Quest showError

WARNING: C:\Documents and Settings\Administrator\Desktop\Lineage 2 Gracia\gameserver\data\scripts\ai\group_template\L2AttackableAIScript.java

java.lang.ClassCastException: net.sf.l2j.gameserver.model.actor.instance.L2MonsterInstance cannot be cast to net.sf.l2j.gameserver.model.actor.instance.L2PcInstance

at net.sf.l2j.gameserver.model.actor.L2Character.doAttack(L2Character.java:688)

at net.sf.l2j.gameserver.model.actor.L2Character$AIAccessor.doAttack(L2Character.java:3392)

at net.sf.l2j.gameserver.ai.L2AttackableAI.thinkAttack(L2AttackableAI.java:1416)

at net.sf.l2j.gameserver.ai.L2AttackableAI.onEvtThink(L2AttackableAI.java:1440)

at net.sf.l2j.gameserver.ai.AbstractAI.notifyEvent(AbstractAI.java:418)

at net.sf.l2j.gameserver.ai.AbstractAI.notifyEvent(AbstractAI.java:361)

at net.sf.l2j.gameserver.ai.L2CharacterAI.onIntentionAttack(L2CharacterAI.java:256)

at net.sf.l2j.gameserver.ai.L2AttackableAI.onIntentionAttack(L2AttackableAI.java:384)

at net.sf.l2j.gameserver.ai.AbstractAI.setIntention(AbstractAI.java:309)

at net.sf.l2j.gameserver.ai.AbstractAI.setIntention(AbstractAI.java:249)

at net.sf.l2j.gameserver.ai.L2AttackableAI.onEvtAttacked(L2AttackableAI.java:1488)

at net.sf.l2j.gameserver.ai.AbstractAI.notifyEvent(AbstractAI.java:421)

at net.sf.l2j.gameserver.ai.AbstractAI.notifyEvent(AbstractAI.java:361)

at ai.group_template.L2AttackableAIScript.onAttack(Unknown Source)

at net.sf.l2j.gameserver.model.quest.Quest.onAttack(Quest.java:554)

at net.sf.l2j.gameserver.model.quest.Quest.notifyAttack(Quest.java:343)

at net.sf.l2j.gameserver.model.actor.L2Attackable.addDamage(L2Attackable.java:795)

at net.sf.l2j.gameserver.model.actor.L2Attackable.reduceCurrentHp(L2Attackable.java:377)

at net.sf.l2j.gameserver.model.actor.L2Attackable.reduceCurrentHp(L2Attackable.java:349)

at handlers.skillhandlers.Pdam.useSkill(Unknown Source)

at net.sf.l2j.gameserver.model.actor.L2Character.callSkill(L2Character.java:6444)

at net.sf.l2j.gameserver.model.actor.L2Character.onMagicHitTimer(L2Character.java:6165)

at net.sf.l2j.gameserver.model.actor.L2Character$MagicUseTask.run(L2Character.java:2523)

at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)

at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)

at java.util.concurrent.FutureTask.run(Unknown Source)

[Zyroh]

please someone that has had success with these kinds of errors check this out please, i can provide more information if you need it.  most everything else works with the exception of this error.  one thing that is wierd the mobs don't attack even if you're not playing in invulnerable mode, i assume it's due to this error, though i could be wrong.